Premium papers are bright, blade-coated papers used in high-end printing applications where multi-color pictures and lettering are applied. There is a great commercial interest in using premium papers to form packages for food products, agricultural products, such as seeds, and other items. However, such papers are prone to penetration by water vapor and oxygen.
Aqueous latexes of polyvinylidene chloride (PVdC) have been used to form moisture and oxygen barrier coatings for many years. Typically, the PVdC is coated onto a substrate and dried using infrared radiation, hot air, or a combination thereof. Often, two layers of PVdC are applied to the substrate to improve the barrier properties of the resulting composite. The composite typically is wound into a roll for later processing. A major drawback with the presently available PVdC coating processes is that, under certain circumstances, the PVdC tends to adhere to the other side of the substrate. Thus, the composite is prone to adhering to itself, or “blocking,” when the roll is unwound.
In the case of premium papers, the side of the paper to be printed typically comprises a coating of inorganic particulates, such as clay, in a binder material, such as an acrylic latex. This side is referred to herein as the “printing” side, which may have a glossy finish, matte finish, or any other finish as desired. To form a barrier material, PVDC is applied to the other side of the paper, referred to herein as the “non-printing” side. When PVDC coated premium papers are dried and wound into a roll, the PVDC on the non-printing side tends to adhere to the printing side of the paper. As a result, the PVdC sometimes “picks” fibers from the printing side of the paper, thereby rendering it unsuitable for printing.
Thus, there remains a need for a method of forming a PVdC coated premium paper having barrier properties, and a roll of such premium paper, that is not prone to blocking.